Electric fence charger

ABSTRACT

A device for periodically applying a high potential on an electric fence has means for applying such potential for very short times at periodic intervals. The time between successive charging intervals depends upon whether the fence is &#39;&#39;&#39;&#39;loaded&#39;&#39;&#39;&#39; (where an animal grounds such fence) or is &#39;&#39;&#39;&#39;unloaded&#39;&#39;&#39;&#39;. If the fence is &#39;&#39;&#39;&#39;unloaded&#39;&#39;&#39;&#39;, the repetition rate of charging pulses is minimized and if the fence is &#39;&#39;&#39;&#39;loaded&#39;&#39;&#39;&#39;, the pulse repetition rate is increased. The change in pulse repetition rate is determined by the fence &#39;&#39;&#39;&#39;loading&#39;&#39;&#39;&#39; reflected into the fence charger system and determines the discharge level of a timing capacitor.

United States Patent Malme v [541 ELECTRIC FENCE CHARGER [72] Inventor:Elmer K.'Mllme, St. Charles, Ill. [73] Assignee: Wire Sales Company,Chicago,'lll. [22] Filed: Feb. 8, 1971 [21] Appl. No.: 113,477

[52] U.S. Cl. ..3 07/l32 R, 256/10, 340/254, i 307/ I06 [5 1] Int. Cl...H0lh 47/00 [58] Field of Search ..307/1 32 R, I32 M, 132 E, I32 ER,307/106, 1 I2, 96; 256/ I0; 340/253, 254

[5 6] References Cited UNITED STATES PATENTS 3,392,285 7/i968Olson.,...l ..'..307/132R [151 3,655,994 Apr.l1, 1972 3,378,694 4/I968Griffeth ..307/l32M Primary Examiner-Herman .I. .HohauserAttorney-Robert L. Kahn [57] I ABSTRACT A device for periodicallyapplying a high potential on an electric fence has meansfor applyingsuch potential for very short times at periodic intervals. The timebetween successive charging intervals depends upon whether the fence isloaded (where an animal grounds such fence) or is unloaded". If thefence is "unloaded", the repetition rate of charging pulses is minimizedand if the fence is loaded, the pulse repetition rate is increased. Thechange in pulse repetition rate is determined by the fence "loading"reflected into the fence charger system and determines the dischargelevel of a timing capacitor.

8 Claims, 9 Drawing Figures Patented April 11, 1972 3,655,994

3 Sheets-Sheet l V 9] 1 Inventor ELM R K. BY E MALME QoJm/f 4/m/ELECTRIC FENCE CHARGER INTRODUCTION This invention relates to a fencecharger and provides a device which is simple, efficient and safe. As iswell known, fence chargers have been known and used for many years toimpress shocking potentials on wire fences to train cattle or animalsgenerally from straying beyond predetermined boundaries. As a rule, suchchargers apply at periodic intervals potentials of the order of severalthousand volts but at low currents. Generally the power output of acharger is low so that cattle, while given a mild shock, will not beinjured and will learn to remain clear of a fence.

Because of possible dangers of electrocution from fence chargers,governmental agencies have imposed requirements on the characteristicsofsuch chargers. For example, it is important that a fence charger operateto charge a fence intermittently. As an example, many chargers willimpress short pulses on a wire fence for less than about oneone-thousandth of a'second every few seconds. In addition, such acharger must operate at a power level too low to be lethal to animalsand must have insufficient energy storage to create an are, which mightstart fires.

Where a charger is energized from a battery, economy of power forcharger operation is important, this determining servicing of a charger.Chargers may be operated from a 115 volt 60 cycle power line. Apart fromminimizing the amount of power required for operating a fence chargerfrom a power line is the added necessity for protection againstimpressing power line voltages accidentally on a fence.

As a rule, fence chargers have poor voltage regulation. Current drawnfrom a fence charger following the initial electric shock will be atgreatly reduced voltage. In general, a fence charger has each shockingcycle independently of preceeding or, subsequent cycles, assuming ofcourse that a charger is operating properly.

GENERAL DESCRIPTION OF INVENTION The present invention to be hereinafterdisclosed provides a fence charger which will normally operate at whatmight be termed a predetermined stand-by repetition rate when .unloaded,as when no cattle are contacting a fence and will operate at a higherrepetition rate when the fence is loaded as when some creature isagainst the fence and is grounding the metal of the fence. As examples,a fence charger operating in conjunction with an unloaded fence may havea repetition rate of about one shocking cycle every three seconds (sucha rate may be specified frequently) and a repetition rate of about oneper second when operating with a loaded fence. The actual duration of ashocking or charging pulse is in the microsecond range.

Fence chargers powered from batteries or from a power line, operateunder severe conditions. Operating conditions may vary from one extreme,in the winter where temperatures and moisture in the form of snow or iceis present to another extreme where high temperatures because ofexposure to direct sun. The various parts making up a charger mustmaintain their operational characteristics within a limited range inregard to both repetition rate and voltage output. The stability of theentire system therefore is important. A system embodying the presentinvention utilizes capacitors, resistors, solid state components(diodes, transistors) and ferro-magnetic devices such as chokes andtransformers.

The new fence charger embodying the present invention provides circuitrywhich insures improved operating stability and provides response tochanges in fence conditions between loaded and unloaded and insures ahigh degree of reliability. A system embodying the present invention haswhat might be termed a basic fence charging system operating under thecontrol of a timing circuit which in turn may be modified by anauxillary control circuit responsive to the load conditions of a fencebeing charged.

The changes in fence conditions between load and no load are such thatthere is a variation not only in the character of the load but also inthe quantitative nature of the load. A fence to be charged may rangefrom a comparatively short length of the order of several hundred feetor less to as much as 15 or more miles. When such a fence is unloaded,and assuming substantial absence of moisture and plant life at thefence, the nature of the load faced by a fence charger output terminalsis generally capacitive. There is ohmic resistance with a great lengthof iron wire but this is negligible. The fence resistance to ground isgenerally great but is greatly reduced when an animal shorts a fence toground. A resistive load may range from several hundred to may thousandohms. Apart from the load characteristics, when considerable water ispresent as in winter so that a bridge of water is between the fence andground, the resistive load may drop to a low value.

THE INVENTION GENERALLY The invention provides a transistorized fencecharger whose normal repetition rate is controlled by a timing circuitof the resistor-capacitor type. So long as a fence is unloaded, theoperation of the charger continues at its normal repetition rate of theorder of about one cycle per 3 seconds as an example. During suchoperation, the charger embodying the present invention senses the fencecondition for change from a normal unloaded condition.

The sensing portion of the system includes auxiliary or monitor circuitsincluding resistors and capacitors. So long as the fence remainsunloaded, the sensing portion of the system is operating and affects therepetition rate of the charger, However, if the sensing portion of thesystem detects a loaded fence condition, then a speed-up in therepetition rate of the fence charger occurs. As an example, from astandby repeti tion rate of one operating cycle during a three secondtime period, the repetition rate may be tripled so that a charging ratewill be increased to one operating cycle per second. It is understoodthat these repetition rates are given by way of example and may havedifferent values depending upon desired conditions.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows in diagrammatic form afence charging system embodying the present invention.

FIGS. 2 to 9 inclusive show oscillographic traces taken from the screenof a double display oscilloscope at various positions in the chargersystem, each of the traces being more fully described later.

DETAILED DESCRIPTION OF THE NEW FENCE CHARGER Step-up transformer 10 hasprimary winding 11 and secondary winding 12 magnetically linked throughiron core 14 of the high leakage type generally used in fence chargers.Transformer 10 has electrostatic shield 13 disposed over primary winding11 to prevent build-up of dangerous potentials in the primary winding.Primary winding 11 has its terminals normally connected through fuses topower line wires 17 and 18 of a conventional ll5 volts, 60 cycle powerline. Lightning arrester 20 is connected across primary winding 11, thearrester having electrodes 21 and 22 on opposite sides of groundedelectrode 23.

Transformer secondary winding 12 has terminals 26 and 27 between whichare connected respectively in series resistor 28, neon light 29 andresistor 30. Resistors 28 and 30 are generally of equal value and as oneexample may each be 220 K ohms. Transformer 10 is of a suitable type andin the case of a volt supply line may have a step-up ratio of the orderof about 2.

Terminal 26 is connected to the positive terminal of diode 32 whosenegative terminal is connected through resistor 33 to junction point 34.As an assumed example, resistor 33 may be about 1500 ohms. From junction34, wire 35 goes to one terminal of storage capacitor 36, the otherterminal of which is connected by wire 37 to junction point 38.Capacitor 36 must be able to withstand the full voltage across secondarywinding 12 and accordingly, should be capable of withstanding a voltageof 450 as an example and preferably have a capacity of about 16microfarads (mf). Capacitor 36 is of the nonpolarized, and may be of theelectrolytic type. Junction point 38 is connected by wire 39 back toterminal 27.

Wire 39 continues beyond junction 38 to and beyond junction point 40.Junction point 40 is connected to the positive terminal of rectifyingdiode 41', whose negative terminal is connected to terminal 42 of choke44. This choke may have a rather low inductance value such as about 300millihenries and tends to stabilize the effects of some fencecapacitance in long fences (as miles). The exact value of this choke isnot critical. Choke 44 has terminal 45 connected to one terminal ofauxiliary capacitor 46. Capacitor 46 need not have a high value ofcapacitance and, as an example, may be a 0.4 mf 600 volt capacitor.Capacitor 46 has its remaining terminal connected to junction point 48.From junction point 48, a connection goes to one terminal of timingcapacitor 50, the remaining terminal of this capacitor being connectedto junction point 52. Junction point 52 is connected to one end ofresistance network 53, the other end of this resistance network beingconnected to junction point 54 on wire 55 connected to junction point34.

Resistance network 53, while shown as a single resistor, usually hasfour substantially equal resistors in series. The purpose of such anarrangement of resistors is to insure that if any one of the resistorsshorts out, the remaining will still function. Each of the equalresistors may be substantially about 360 K ohms, making a total of about1440 K ohms.

Referring back to timing capacitor 50, this is a rather large capacitorsuch as about or 22 mt but in the example given I 7 terminal connectedto junction point 63 which in turn is connected to junction point 48.The gate electrode of SCR 61 is connected by wire 65 to junction point66. Junction point 66 in turn is connected through resistor 67, having acomparatively low value such as about 100 ohms, to junction point 63awhich is connected to or may be at junction point 63. Junction point 63ahas connected thereto one terminal of resistance element 68 forming partof a potentiometer, the other terminal of the resistor being connectedto junction point 45. Forming part of the potentiometer and cooperatingwith resistor 68 is wiper 68a connected to one terminal of diac 70,whose remaining terminal is connected back to junction point 66.

A diac is a two-electrode, three layer bi-directional avalanche diodewhich can be switched from the OFF state to the ON state for eitherpolarity of applied voltage. For further details on a diac and itscharacteristics and structure, reference is made to RCA book entitledTransistor, Thyristor and Diode Manual published by Radio Corporation ofAmerica in 1969, pages 43 and 44. The potentiometer and diac (in thisinstance a simple diode having a predetermined breakdown value may beused) with resistor network will determine the breakdown potential orfiring of SCR 61.

Wire connection 72 between junction points 63 and 48 continues tojunction 73. From junction point 73 wire 730 goes to the negativeelectrode of SCR 75, the positive terminal of which is connected tojunction point 76 on wire 55. The gate electrode for SCR 75 is connectedby wire 77 to one terminal of diac 78, the other terminal of which isconnected through resistor 80 to junction point 52. Resistor 80 has acomparatively low value, such as for example about 68 ohms.

Providing a shunt between junction points 73 and 76is diode 82 whosepositive terminal is connected to junction point 73 and whose negativeterminal is connected through resistor 84 to junction point 76. Resistor84 is also a relatively low resistor in this particular instance beingabout 100 ohms.

Returning to junction point 73, a wire connection goes to primarywinding 88 of pulse type transformer 89. Pulse type transformer 89 hassecondary winding 90 whose terminals are connected respectively togrounded terminal 92 and load (wire fence) terminal 93. Shunted acrosssecondary winding 90 is neon light 94 in series with ballast resistor95. Preferably, the arrangement is such that one terminal of the neontube is grounded. Resistor 95 functions as a ballast for the neon bulband has a suitably high value. As a rule, such resistors will have avalue of the general order of about 1 megohm, the exact value beingdetermined by the type of neon bulb, operating voltage output and thelike.

As is well known, a pulse type transformer is adapted to receive a steepvoltage pulse impressed upon the primary winding and to emit a sharppulse from the secondary winding. As a rule, the output potential ofsecondary winding 90 will be in the order of several thousand volts.However, the time duration of such pulse is extremely short but at verylow currents in the milleampere range.

The new fence charger may be adapted for battery operation by theconventional expedient of converting the battery direct current tointerrupted current, stepping the interrupted voltage to a desired highvalue by a transformer and charging capacitor 36 to an appropriatevoltage. As a rule, a transistorized blocking oscillator having arepetition rate of say about 200 or 300 per second may be used with thebattery supplying the input and the output energizing a step-up transformer corresponding in function to transformer 10. The remainder of thesystem may be generally similar to the system so far described. Thevalues of components and potentials may differ due to optimizing batterylife.

OPERATION OF THE SYSTEM The operation of a system embodying the presentinvention is based upon the fact that normally a fence to be chargedpresents a very high resistance capacitive load when the fence isunloaded." The average fence may have a capacitance of from about 0.015micro farads to as much as 0.1 mf or even higher depending upon thelength of the fence. This is on the assumption that the fence is dry,has no animal to load the fence and has no water, snow, weeds or thelike to reduce the resistance of the fence system. When an animal ispresent and loads]the fence, a resistance of the order of severalthousand ohms to as much as about 100,000 ohms may be seen from theoutput of the pulse transformer.

Assuming that the fence is unloaded, the secondary of the pulsetransformer will see a high ohmic resistance. In this connection, caremust, be exercised to be sure that the ballast resistor for the neonlight across the output of the pulse transformer secondary winding ishigh, in the actual example given, this being almost one megohm. Undersuch conditions, capacitor 36 will charge substantially to its fullpotential within a few cycles (if 60 cycle operation is assumed). Thusthe potential of junction point 54 will rise to an appropriate valuesuch as, for example, 325 volts in'the assumed example. Resistancenetwork 53 will permit a small current to flow to junction point 52.

If timing capacitor 50 is fully discharged, the potential of junctionpoint 52 will rise from zero or ground (junction point 73 may be assumedto be ground) in about 2% or 3 seconds and will, after breakdown ofbarrier device 78, cause the potential of wire 77 to the gate electrodeof SCR 75 to reach a value of about 30 or 35 depending upon thecharacteristics of potential barrier device 78. For the voltagesinvolved, the gate electrode potential will be adequate to trigger SCR75 to conduction. Capacitor 36 will thereupon discharge a heavy currentthrough SCR 75 to junction point 73 and thence through primary winding88 of the pulse transformer, to junction point 38 and wire 37 to thenegative terminal of capacitor 36. The cut-in potential of barrierdevice 78 will, in this instance, be about or and the cut-out potentialof device 78 will be about 6 volts lower. While discharge current isgoing through SCR 75, it should be noted that timing capacitor 50 willalso discharge some current through current limiting resistor 80, 78,and SCR 75 to junction point 73 and thence to the remaining terminal oftiming capacitor 50.

The heavy discharge current through SCR 75 and through the primarywinding of the pulse transformer will result in the sudden creation of astrong magnetic field for generating a high potential in pulsetransformer secondary 90. The high resistance seen by pulse secondary 90will permit cooperation between the energy stored in the magnetic fieldof the pulse transformer and the energy stored of the electric field incapacitor 36. The result will be a discharge through SCR 75 which hasthe characteristics of a resonant peak or wave for at least one-halfcycle. The energy stored in the magnetic field of primary winding 88when the field collapses tends to keep current flowing in the samedirection (the polarity is now reversed) so that capacitor 36 will notonly discharge completely but may even by partially charged withreversed polarity for a short time. At the same time, the self-inducedhigh voltage generated in primary winding 88 of the pulse transformerwill pass through rectifier 41 and through choke 44 and will tend tocharge auxiliary capacitor 46 so that the terminal of this capacitorconnected to choke terminal 45 will be positive.

The shock effects in the system, particularly the resistance networkassociated with SCR 61, results in this latter device conducting andpractically short circuiting timing capacitor 50. The discharge oftiming capacitor results in the potential of junction point 52 going tozero with reference to junction point 73. Thus at the end of about 3seconds from the beginning of the initial charging of capacitor 36, thesituation is as follows SCR 75 is non-conducting; capacitor'50 isdischarged fully; auxiliary capacitor 46 may be charged as indicated;SCR 61 is non-conducting and capacitor 36 is completely discharged.

Rectifier 82 protects SCR against reverse voltage. Choke 44 will providedesirable control action when the pulse from transformer primer 88results from the decay of the magnetic field (this tending to keep thecurrent flowing). Auxiliary capacitor 46 will discharge throughresistance element 68 of the potentiometer just slowly enough tostabilize the trigger action on SCR 61.

Thus, a relaxation type of oscillator action involving capacitor 36cooperates with an auxiliary relaxation type of oscillator only when thelatter is triggered by the apparent existence of some resonance betweencapacitor 36 and primary winding 88 during discharge of SCR 75. If theresistance seen by pulse transformer secondary 90 is low enough so thatthe reflected resistance into the primary circuit militates againstresonance, then the following action occurs. Capacitor 50 cannotdischarge very much through SCR 75 and the potential of junction point52 will drop enough (about 6 volts in this instance) to cut off the gateelectrode for SCR 75. The discharge of capacitor 36 through SCR 75 isfast enough so that capacitor 36 is completely discharged. The dischargethrough SCR 75 is very short, such as about 300 micro seconds, duringwhich time, timing capacitor 50 can discharge slightly. The time forre-charging timing capacitor 50 after its partial discharge is such thatthe potential of junction point 52 will rise to maximum value withinabout one second, thus making the repetition rate for the entire system1 per second.

Insofar as barrier device 78 is concerned, the cut-in potential in thedirection of conduction to the gate of 75 will be between about 30 and35 volts and the cut-out potential for this same device will be about 6volts lower, making it about 29 volts. Thus the potential of junctionpoint 52 will vary between about 35 volts and about 29 volts with thecharging period for timing capacitor 50 being about one second. Barrierdevice 78 in this particular system should preferably have desirable anddefinite cut-in and cut-out voltage values for dependable andcontrollable repetition rate when the fence is loaded. Barrier device 70associated with SCR 61 should have a desired voltage cut-in point in thedirection of conduction from wiper 68a to the gate electrode of SCR 61.The cutout point is zero. With the system as shown, the lower that wiper68a is adjusted along resistor 68 away from junction point 63, thegreater is the feedback potential to the gate electrode of SCR 61 andthe greater the stability of operation as between loaded" and unloaded"conditions.

With reference to barrier or trigger device 70, for the system as setforth in the example given, a so-called silicon bilateral switch made byGeneral Electric Company, Part No. 2N499l has been used. It happens thatthis device has three electrodes and can control conduction in eitherdirection. However, the requirements of the new charger system are suchthat conductivity in only one direction is necessary, the

direction of positive current flow being toward the gate electrode ofSCR 6]. This particular device on the market has the desired barrierpotential characteristics to block the flow of current in the desireddirection for voltages of from about 6 to about 9 volts. Current flow inthe desired direction will continue until the voltage drops topractically zero, the particular cutoff voltage being unimportant inthis particular application of the switch.

Substantially the same considerations apply to disc 78, the desireddirection of positive current flow in this instance being from junctionpoint 52 to the gate of SCR 75. No flow in the reverse direction isdesired or necessary. With respect to diac 78, a trigger or diac deviceNo. S-032 made by Hunt Electric Company is available on the market. Inthe charger example given, diac 78 happens to cut-in or trigger at fromabout 28 to about 35 volts and will cut-off at about 6 volts below thetrigger point. These values for diacs 78 and 70 are convenient for theparticular example of the charger system involved here. Simple diodeshaving desired barrier potentials may be used or desired bias diodesystems may be used.

In each instance, the diac is used as a diode conducting in only onedirection and normally having a breakdown voltage as previously setforth. It is therefore understood that devices 70 and 78 respectivelymay be conveniently replaced by simple diodes having desired operatingcharacteristics with regard to breakdown voltage in the direction ofconduction and, of course, having satisfactory reverse potentialcharacteristics.

With respect to capacitor 46, the circuitry involving capacitor 46,choke 45 and the resistor network is such that the inductive emfgenerated in the pulse transformer makes it necessary for capacitor 46to withstand high potentials and in the particular example given, a 600volt non-electrolytic capacitor of the non-polarized type isrecommended.

In connection with the pulse transformer, as is well known, lowinductance in the millihenry range is present. Thus, a pulse transformerhaving a primary inductance of the order of about 16 mh was used (thesecondary was open) and an inductance of about 6 Henries in thesecondary with the primary winding open. A pulse transformer of thisgeneral character is widely used in the fence charger art. It isunderstood, however, that variations may be made in the inductances ofthe pulse transformer and that variations may be made in the cutin andcut-off values of the various solid state switches. In practice, thevoltage characteristics of the SCR devices must be such that suitablecontrol of the breakdown values of such devices must be exercised. Insome instances, underwriter laboratories and insurance requirements maydictate certain values such as, for example, the repetition rate of acharger, the value of storage capacitor 36, the output potential of thepulse transformer and the like.

Referring now to FIGS. 2 to 9 inclusive, these show oscillographictraces of voltage or current variations with respect to time of a fencecharger embodying the present invention whose components substantiallyhave the values previously given by way of example. The traces weretaken on an oscilloscope having means for substantially simultaneouslyexhibit ing two separate traces as hereinafter described.

FIG. 2 shows a fence charger operating with a 16 mile long fence orequivalent. In the top trace, the fence was loaded with a 100K resistorso that the charger was loaded. The sawtooth top trace shows that theSCR 75 was conducting, in this instance, at intervals of a bit less than1.5 seconds. The voltage trace taken across timing capacitor 50 showsthat the potential of junction point 52 with reference to junction point48 would range between 22 and about 28 volts. This indicated that SCR 61was not breaking down and that timing capacitor 50 was discharginglightly during the time that SCR 75 was conducting.

The lower voltage trace in FIG. 2 indicates that the voltage acrosscapacitor 50 would range from a minimum of substantially zero to amaximum of about 27 or 28 volts. Because timing capacitor 50 completelydischarged, the sawtooth wave indicating a longer charging time resultedin an unloaded repetition rate of approximately once per four seconds.This unloaded repetition rate clearly indicates that SCR 61 was not onlyfunctioning to short timing capacitor 50 but shows that the freeunloaded running rate is about one-third of the loaded repetition rate.The 16 mile fence load was connected to 220K ohms resistance forsimulating an unloaded fence.

The left beginning of each voltage trace shows a practically verticalvoltage drop resulting from the sudden discharge at SCR 75. The upwardlysloping voltage curve indicates that SCR 75 has cut-off and that thepotential of junction point 52 is beginning to climp up again at a ratedetermined by the time constant of the system. The entire charger systemis so designed that SCR 75 breaks down before the capacitor chargingcurve begins to assume the normal curved shape in cident to a fullcharge in a capacitor. In short, the part of the voltage charging curveused here is the lower straight portion, this being common in manycapacitor charging circuits.

Referring now to FIG. 3, the two curves show the charger operating withload equivalent to 16 miles of fence and having a loading resistor ofsubstantially 100K ohms. In this particular instance, the 16 miles offence is roughly equivalent in capacitance to a 0.25 mf and serve toload the charger. The top trace shows the voltage across primary winding88 of the pulse transformer while the bottom trace shows the currentpassing through SCR 75 at breakdown. As the top trace shows, the voltageacross primary winding 88 drops rapidly from an original voltage ofabout 280 volts when SCR 75 begins to break down to zero and drops belowzero and then levels off about 30 or 40 volts during the time thatcapacitor 36 is re-charging. Up to the time that SCR 75 breaks down, thepotential of junction point 73 is isolated so that there is little, ifany, potential across primary winding 88. However, when SCR 75 breaksdown, the various capacitors and resistors in a system together with thecapacitance of the fence load and the inductance of the pulsetransformer all cooperate to have storage capacitor 36 over-dischargeand reverse charge to some extent. The heavy current indicated by thelower trace shows the characteristic pulse pattern resulting from thebreakdown of SCR 75 and shows the current pulse applied to the pulsetransformer winding. The charger load in this instance is heavy enoughso that the charger is loaded" and SCR 61 does not break down.

FIG. 4 shows the voltage curve across the primary winding of the pulsetransformer. Again the beginning or left end of the trace shows thecharacteristic sudden drop of voltage when SCR 75 breaks down. In thisparticular instance, the bottom portion of the voltage drop shows thenegative voltage pulse after which the voltage flattens out from a valueabout plus 40 to and then drops below 0 and finally stabilizes at about0. The curves in FIG. 4 are from a charger having a 16 mile fence load.The lower trace shows the fence charger both loaded and unloaded asmarked.

The lower trace shows the potential across timing capacitor 50. With thecharger loaded with 100K ohms, the potential across the timing capacitor50 goes from about 28 or so volts down to about 22 volts and remains atthat value for the balance of the operating period. The trace shows,however, when a 220K ohm load was used (the charger is now unloaded), ashort instant of time after the discharge of SCR 75, SCR 61 triggers andthe voltage across timing capacitor 50 rapidly drops to 0. Due tochanges in the length and capacitance of a fence as well as the amountof resistance faced by the output pulse transformer, the time after SCR75 discharges when auxiliary SCR 61 discharges may vary. This involvessuch considerations as the interaction between the pulse transformer andthe capacitance of storage capacitor 36 and the resistor networksassociated with both SCRs.

FIG. 5 illustrates the voltage conditions across the primary of thepulse transformer, this being generally similar to the top trace of FIG.4. However, the bottom trace of FIG. 5 shows the potential acrosscapacitor 46. This .4 mf capacitor 46 shows some lateral displacement ofthe potential curves along the time axis with respect to capacitor 46when the charger as a whole is unloaded" and loaded respectively.Resistance 220K ohms keeps the charger system unloaded whereas the Kohms is low enough so that the system is loaded". In the lower traces ofFIG. 5, the left or beginning of the trace shows the effect of thepresence of choke 44. Thus a sharp initial pulse across capacitor 46 isdue to the action of the choke. By contrast, note in FIG. 9, thesubstantial potential peak due to the absence of a choke. The choke isparticularly desirable when a long fence such as 16 miles is beingcharged.

The lateral displacement of the potentials across the .4 microfaradcapacitor shown in the lower trace in FIG. 5 is due to the differencesbetween the loaded and unloaded fence charger operation.

Referring now to FIG. 6, this shows the operation of the charger systemwhen the fence load was one mile. Such a load does not have very muchcapacitance (about 0.015 mf). Thus the primary voltage illustrated inthe top trace is generally similar to the top traces in other figureswith some displacement along the time axis. However, the two lowertraces showing the loaded and unloaded conditions are generally similarto the curves shown in FIG. 4 with the exception that the breakdown ofSCR 61 appears to occur much faster. It is thus evident that changes inthe fence length as well as resistance will all have their effects inrelative displacement along time axes.

Referring now to FIG. 7, this shows voltage traces across the trigger orbarrier diac 70. Thus with 100,000K ohm (charger loaded) the voltageacross capacitor 46 is too low and will not permit SCR 61 to operate.However, when capacitor 46 has sufficient voltage across is (this willoccur when the charger is sunloaded with a sufficiently highresistance), the potential across barrier device 70 will be high enoughto cause breakdown so that the potential of the gate electrode for SCR61 rises to the breakdown value. SCR 61 will conduct and shortcircuitcapacitor 50. It is clear that the traces are in some respectsdiscontinuous because of the action of the barrier characteristics.Thus, for example, the lowest trace in FIG. 7 is simply a straighthorizontal line showing a voltage of something less than one volt. Theleft or beginning of this bottom trace probably should join up to thehorizontal or initial portions of the traces at or somewhat below 0volts. The next trace reflecting the action due to 100,000 ohms shows arapid rise in potential but continues past the peak to drop off ascapacitor 46 discharges across the potentiometer resistor. However, thetwo plots that show almost vertical rises from 0 to almost 8 volts arecontinuous due to the sudden breakdown of SCR 61. It is important thatcapacitor 46 discharge before a new sawtooth wave begins.

Referring now to FIG. 8, the top trace shows the primary voltage atinitial breakdown of SCR 75 with the voltage going down to 0 and to anegative value. At times, the negative pulse at the beginning of thetrace may also result in a short negative pulse somewhat later andbefore the next initiation of a working cycle. The lower trace shows thepotential across capacitor 46. At the beginning, the voltage is 0 orsubstantially zero and quickly rises to about 1 volt. This action occurswith choke 44 and particularly with a long fence. In this particularinstance the fence load was 16 miles with the resistance having a valueof about 100K ohms. This is equivalent to tion on the charger. FIG. 9,however, is the same system with the same load except that choke 44 isremoved. The large amount of capacitance present with a 16 mile fencecauses a potential across capacitor 46 to jump to a substantially highvalue, 60 volts, after which the voltage gradually discharges. This isundesirable since there will be erratic operation with respect to thecharger changing its repetition frequency between loaded and unloaded"conditions.

Due to transient conditions inherent in the operation of the systemunder various conditions, some changes in voltage traces, time periodsand the like are bound to occur. By adjustment of potentiometer wiper68a and other components, satisfactory operation of a charger embodyingthe present invention may be obtained within satisfactory limits. As anexample, the choke may be omitted if the charger will not be used onlong fences. in addition, the characteristics of the pulse transformerin regard to inductance, and the characteristics of the various diodesand other solid state devices with regard to breakdown or triggervoltages and the characteristics of the various capacitors will all havesome efiect on the operation of the system. However, for the most part,precision as to the duration of a period between successive pulses isnot necessary as a rule so that considerable tolerances will bepennissible.

What is claimed is:

1. An electric fence charger for intermittently charging a fence to ashocking potential, said charger including a first storage capacitor,means for charging said first storage capacitor to a predetermined highpotential within a fraction of a second, a first solid state devicehaving positive,negative and gate electrodes, a wire connection fromsaid negative electrode to a first junction point, a pulse step-uptransformer having primary and secondary windings, a direct connectionfrom one terminal of said primary winding to said first junction point,a direct wire connection from the other terminal of said primary windingto the other terminal of said first capacitor, a first resistor networkconnected between said positive electrode and gate electrode, said firstresistor network including a direct current non-conducting barrierdevice having a predetermined breakdown potential, said first resistornetwork including a second junction point with said barrier devicedisposed between said second junction point and said gate electrode, asecond (timing) capacitor connected between said two junction points, asecond solid state device having positive, negative and gate electrodes,a direct wire connection from said second device negative electrode tosaid first junction point, a direct current connection between saidsecond device positive electrode and said second junction point, asecond resistor network including a rectifier device having apredetermined voltage breakdown value in the conducting directionbetween the gate and negative electrodes of said second device, a thirdauxiliary capacitor connected across a portion of said second resistornetwork, said third capacitor having one terminal connected to saidfirst junction point and having the other terminal connected through awire connection to the negative terminal of a rectifier, said rectifierhaving its positive terminal connected to the other terminal of saidpulse transformer primary winding, said system having the portionsthereof cooperating so that when the pulse transformer secondary windingfaces a sufficiently high resistance, the discharge of said first solidstate device causes said second solid state to discharge completely saidsecond capacitor whereby recharging said second capacitor requiresmaximum recharge duration (and consequent minimum pulse repetitionrate), said charger, when facing a lower resistance, operating to permitsaid first solid state device to discharge without discharge of saidsecond solid state device, said second capacitor discharging onlypartially through said first device and thus a loaded" condiincrease thepulse and repetition rate.

2. The system according to claim 1 wherein said first capacitor and saidtiming capacitor each have values of over 10 microfarads, said firstcapacitor being of the non-polarized type, said third capacitor having avalue of a lower order than either of said first or second capacitors.

3. The system according to claim 2 wherein a choke is connected betweenthe negative terminal of said first named rectifier and the otherterminal of said third capacitor, said choke having a value in themillihenry range for reducing the self-inductive pulse from the primarywinding of the pulse transformer after shut-ofi of said first solidstate device.

4. The system according to claim 1 wherein a second rectifier andcurrent limiting resistor are connected across said first solid statedevice, the polarity of said second rectifier being reverse of saidfirst device, said second rectifier having a sufficiently high breakdownvalue to protect said first device against reverse potential originatingin said pulse transformer primary winding.

5. The system according to claim 1 wherein said resistance networkassociated with said second device comprises a current limiting resistorbetween said'first junction point and the positive electrode of saidsecond device, a second current limiting resistor connected between thegate and negative electrodes of said second device, a potentiometerresistor element connected across said third capacitor, saidpotentiometer resistor having a wiper associated therewith connectedthrough said second trigger barrier device to the gate electrode of saidsecond device, said second barrier trigger device having a predeterminedbreakdown potential in the direction of current fiow from the wipertoward said gate electrode, said first barrier trigger device connectedto said gate electrode of said first solid state device havingpredetermined cut-in and cut-out potentials in the direction of currentflow from said first junction point to the gate of said first device.

6. The system according to claim 5 wherein a choke in the millehenryrange is connected between the negative electrode of the first rectifierand the common terminal of said potentiometer resistance and terminal ofsaid third capacitor.

7. The system according to claim 6 wherein the resistance element ofsaid potentiometer has a sufficiently high value so that said thirdcapacitor, when charged from the operation of the pulse transformerprimary winding, will discharge slowly enough so that substantially nochange in the potential across the same will occur during the suddenprecipitant change in potential conditions in the system incident to thedischarge of either of said devices but instead will discharge over thesubstantial portion of a sawtooth wave.

8. A fence charger system comprising a sawtooth wave generator includinga primary winding of a pulse transformer, said generator also includinga resistor for determining a repetition rate for sawtooth wavegeneration, a timing capacitor connected between two point in saidgenerator, said two points being so disposed as to have potentialdifferences therebetween available for charging said timing capacitor,the level of charge in said timing capacitor having an effect upon therepetition rate of said generator system, said pulse transformer havinga secondary winding for connection to a fence and ground and meansresponsive to the loading on said secondary winding with regard to highresistance corresponding to a normally unloaded fence and lowerresistance corresponding to a normally loaded fence for changing thecharge level in said timing capacitor and thereby changing thedifference in potential between said two points in said generatorsufficiently to increase the repetition rate of said sawtooth generatorwhen said pulse transformer secondary winding sees a loaded fence and todecrease substantially the pulse repetition rate when said secondarywinding sees an unloaded fence, the pulse repetition rates beingsufficiently different so that substantial changes in operating powerfor the charger occur.

it i i i

1. An electric fence charger for intermittently charging a fence to ashocking potential, said charger including a first storage capacitor,means for charging said first storage capacitor to a predetermined highpotential within a fraction of a second, a first solid state devicehaving positive, negative and gate electrodes, a wire connection fromsaid negative electrode to a first junction point, a pulse step-uptransformer having primary and secondary windings, a direct connectionfrom one terminal of said primary winding to said first junction point,a direct wire connection from the other terminal of said primary windingto the other terminal of said first capacitor, a first resistor networkconnected between said positive electrode and gate electrode, said firstresistor network including a direct current nonconducting barrier devicehaving a predetermined breakdown potential, said first resistor networkincluding a second junction point with said barrier device disposedbetween said second junction point and said gate electrode, a second(timing) capacitor connected between said two junction points, a secondsolid state device having positive, negative and gate electrodes, adirect wire connection from said second device negative electrode tosaid first junction point, a direct current connection between saidsecond device positive electrode and said second junction point, asecond resistor network including a rectifier device having apredetermined voltage breakdown value in the conducting directionbetween the gate and negative electrodes of said second device, a thirdauxiliary capacitor connected across a portion of said second resistornetwork, said third capacitor having one terminal connected to saidfirst junction point and having the other terminal connected through awire connection to the negative terminal of a rectifier, said rectifierhaving its positive terminal connected to the other terminal of saidpulse transformer primary winding, said system having the portionsthereof cooperating so that when the pulse transformer secondary windingfaces a sufficiently high resistance, the discharge of said first solidstate device causes said second solid state to discharge completely saidsecond capacitor whereby recharging said second capacitor requiresmaximum recharge duration (and consequent minimum pulse repetitionrate), said charger, when facing a lower resistance, operating to permitsaid first solid state device to discharge without discharge of saidsecond solid state device, said second capacitor discharging onlypartially through said first device and thus increase the pulse andrepetition rate.
 2. The system according to claim 1 wherein said firstcapacitor and said timing capacitor each have values of over 10microfarads, said first capacitor being of the non-polarized type, saidthird cApacitor having a value of a lower order than either of saidfirst or second capacitors.
 3. The system according to claim 2 wherein achoke is connected between the negative terminal of said first namedrectifier and the other terminal of said third capacitor, said chokehaving a value in the millihenry range for reducing the self-inductivepulse from the primary winding of the pulse transformer after shut-offof said first solid state device.
 4. The system according to claim 1wherein a second rectifier and current limiting resistor are connectedacross said first solid state device, the polarity of said secondrectifier being reverse of said first device, said second rectifierhaving a sufficiently high breakdown value to protect said first deviceagainst reverse potential originating in said pulse transformer primarywinding.
 5. The system according to claim 1 wherein said resistancenetwork associated with said second device comprises a current limitingresistor between said first junction point and the positive electrode ofsaid second device, a second current limiting resistor connected betweenthe gate and negative electrodes of said second device, a potentiometerresistor element connected across said third capacitor, saidpotentiometer resistor having a wiper associated therewith connectedthrough said second trigger barrier device to the gate electrode of saidsecond device, said second barrier trigger device having a predeterminedbreakdown potential in the direction of current flow from the wipertoward said gate electrode, said first barrier trigger device connectedto said gate electrode of said first solid state device havingpredetermined cut-in and cut-out potentials in the direction of currentflow from said first junction point to the gate of said first device. 6.The system according to claim 5 wherein a choke in the millehenry rangeis connected between the negative electrode of the first rectifier andthe common terminal of said potentiometer resistance and terminal ofsaid third capacitor.
 7. The system according to claim 6 wherein theresistance element of said potentiometer has a sufficiently high valueso that said third capacitor, when charged from the operation of thepulse transformer primary winding, will discharge slowly enough so thatsubstantially no change in the potential across the same will occurduring the sudden precipitant change in potential conditions in thesystem incident to the discharge of either of said devices but insteadwill discharge over the substantial portion of a sawtooth wave.
 8. Afence charger system comprising a sawtooth wave generator including aprimary winding of a pulse transformer, said generator also including aresistor for determining a repetition rate for sawtooth wave generation,a timing capacitor connected between two point in said generator, saidtwo points being so disposed as to have potential differencestherebetween available for charging said timing capacitor, the level ofcharge in said timing capacitor having an effect upon the repetitionrate of said generator system, said pulse transformer having a secondarywinding for connection to a fence and ground and means responsive to theloading on said secondary winding with regard to high resistancecorresponding to a normally ''''unloaded'''' fence and lower resistancecorresponding to a normally ''''loaded'''' fence for changing the chargelevel in said timing capacitor and thereby changing the difference inpotential between said two points in said generator sufficiently toincrease the repetition rate of said sawtooth generator when said pulsetransformer secondary winding sees a ''''loaded'''' fence and todecrease substantially the pulse repetition rate when said secondarywinding sees an ''''unloaded'''' fence, the pulse repetition rates beingsufficiently different so that substantial changes in operating powerfor the charger occur.